Display screen or portion thereof with a graphical user interface



The FIGURE is a front view of a display screen or portion thereof with a graphical user interface showing our new design.

The outermost broken line rectangle shows the display screen or portion thereof. All other broken lines show portions of the graphical user interface and form no part of the claimed design. 

CLAIM I claim the ornamental design for a display screen or portion thereof with a graphical user interface, as shown and described. 